A study funded by the NC3Rs explored how handling methods influenced mice’s behavior during cognitive tasks

Mice were either picked up by the tail or guided into a tunnel, then transferred to the testing arena

Mice that were transferred in the tunnel were far more exploratory during the cognitive task

Acclimation to handling procedures is important

A published today in Scientific Reports shows that the way experimenters pick up mice can affect their behavior during cognitive tasks. The study was funded by the NC3Rs, which is dedicated to replacing, refining, and reducing the use of animals in research and testing. This particular study focused on refinement: identifying optimal handling methods for mice has important implications for both the welfare of the animals and the validity and usability of data that are collected, which could potentially lead to a reduction in the need for animals in future studies.

Image Credit: Jane Hurst, University of Liverpool.

Drs. Kelly Gouveia and Jane Hurst first placed laboratory mice near a new, attractive stimulus – urine from a novel mouse of the opposite sex – that is known to stimulate approach and investigation. The mice were allowed three sessions to grow accustomed to the new scent. Throughout all three sessions, mice were either picked up by the tail (standard laboratory practice, though there is no obvious scientific reasoning for this method) or were guided into a clear tunnel that is both affordable and easily sterilized. (The method is also .) Mice were then carried to the test arena either by the tail or in the tunnel and allowed to explore. Gouveia and Hurst report that mice picked up by the tail showed very little willingness to explore the test arena, and therefore investigate the new stimulus, whereas those transported in the tunnel showed much higher exploration and a strong interest in the new scent.

Importantly, Gouveia and Hurst then tested the mice’s ability to discriminate between the (formerly) new scent and a second, different urine stimulus. They report that since the mice picked up by the tail performed so poorly from the start, they did not discriminate between the two scents. However, those transported in the tunnel showed robust and reliable discrimination. These findings are noteworthy not only with respect to the psychological welfare of the animals, but also for the important effects that handling and habituation have on yielding usable, reliable data. With the potential to reduce the stress associated with handling, the tunnel method could reduce the anxiety that mice display upon tail handling – thereby resulting in more species-typical behaviors, such as exploration of a novel, conspecific scent. It could also reduce the uncontrolled variation that in and could ultimately produce more reliable data. Thus, identifying optimal handling techniques has the potential to reduce the number of animals needed in laboratory studies in addition to refining the techniques used to study them and enhance their welfare.

Image Credit: Jane Hurst, University of Liverpool.

It is worth noting that a by Novak and colleagues (2015) found no difference in cognitive performance between mice that were handled by the tail or by a less invasive method (“cupping” in the experimenter’s hands). Why might no difference have been found in this study? One possibility is that the cognitive task the researchers used was different from the present study (a radial arm maze vs. novel scent), and the arm maze may probe for different behaviors than a novel odor task. Another possibility is that perhaps mice “prefer” the tunnel to both tail handling and cupping, but neither the 2015 nor the present study compared all three methods. Hurst and her colleague Rebecca West did compare all three methods in a , however, and found that mice preferred both the tunnel and cupping method to tail handling (as assessed by voluntary interaction time with the experimenter); although the cupping method produced more variable results depending on strain and sex. However, in the Novak study, mice were handled daily for many weeks, whereas in the Hurst & West study they were handled only for nine days. Of course, the most parsimonious explanation is that in every handling study, experimenter interaction is confounded with handling. That is, are the mice acclimating to the experimenters, to the handling procedures, or both?

These questions underscore the need for replication before firm conclusions about optimal handling techniques can be drawn. Nevertheless, the findings published today in Scientific Reports are an important addition to the field of animal welfare, and they emphasize the importance of constant, rigorous studies surrounding welfare issues.